The transfer length is the distance required to develop the full capacity of a strand, under service loads, from a value of 0% at the end of the beam (or end of debonding, if present) to 100% of its capacity. For locations within this region, a bi-linear interpolation is performed to compute the effective area of steel.

The basic transfer length is 60 db, as per Art. 5.11.4.1. The development length is the distance required to develop the full capacity of the strand and it is used for ultimate capacity calculations under factored loads. Since the stress under factored loads is higher, the development length is longer than the transfer length. For locations within the region between transfer length and development length, a linear interpolation is performed to compute the effective area of steel. Development length as per Art. 5.11.4.2 is:

• US Units:

• Metric Units:

where:

d_b = Nominal strand diameter, in (mm)

f_ps = Average stress in prestressing steel at time for which nominal resistance of a member is required, ksi (MPa)

f_pe = Effective stress in prestressing steel after losses, ksi (MPa)

Four multipliers have been provided to simulate varying the effective transfer and development lengths for bonded and debonded strands. The default values of the development length multiplier for debonded strands have been preset to 2.0 for compliance with LRFD Art. 5.11.4.3.